THE CAUSE OF BLACK DISEASE. 25 



admitted at once that if the fluke is capable of acting as a mechanical 

 carrier of one species of bacterium to the liver, there is no reason why other 

 species may not be so transmitted, given the opportunity. The writer there- 

 fore hopes that this aspect of the method of infection in the type of disease 

 discussed in the present article may be given consideration by workers on 

 braxy and bradsot, and also in the condition met with in various parts of 

 Australia and elsewhere, in order that the writer's hypothesis may in their 

 particular cases be either established or disproved. 



SUMMARY. 



Black disease is a condition apparently peculiar to sheep, and seasonal in 

 occurrence. 



It is a toxaemia, running an acute course. The primary lesions are 

 situated in the liver, and consist of circumscribed areas of necrosis. One or 

 several lesions may be present. 



Other lesions seen elsewhere must be looked upon as secondary and 

 probably due to the action of the toxin produced by the bacilli in the 

 primary lesion and distributed in the blood stream. 



The primary hepatic lesions contain the causal organism, which at the 

 time of death are confined thereto and cannot be demonstrated elsewhere 

 even in the liver, save for a few exceptional occasions in which no gross 

 necrotic foci were seen but the .bacilli were found to be present in that 

 organ. Such cases may be looked upon as ones of mass infection, the 

 defences of the organ having been overwhelmed before they could come- 

 into action. 



The causal organism is one of the larger anaerobic bacilli, which sporu- 

 lates readily, and is probably a facultative parasite. 



Experimental inoculation of virulent cultures is fatal to sheep and other 

 animals, and the lesions are anatomically those of black disease, the- 

 apparent difference being due to the port of entrance of the bacilli and the 

 nature of the tissues there. (Compare contagious bovine pleuro-pneumonia.) 



The situation of the primary lesion or lesions, and the failure to infect 

 by feeding experiments with virulent cultures or viscera of affected animals, 

 suggests the probability of a carrier, and the seasonal character of the dis- 

 ease, the geographical features of infected paddocks and the presence of 

 fluke disease, indicates that the liver fluke is the mechanical carrier. 



Black disease is probably identical with the braxy -like diseases in Tas- 

 mania and Victoria, although the organism claimed to be the cause of the 

 latter is not identical with that isolated from the former. Until more 

 definite information is obtainable regarding braxy or bradsot, in which the 

 possibility of post-mortem invasion has been eliminated, it is not possible 

 to decide whether the European disease is the same as that seen in Aus- 

 tralia. It is, however, quite probable that it is. 



[The accompanying photographs are by Mr. R. Grant, Bureau of Microbiology.} 

 f 38219 C 



